The present invention relates to ink jet printers and, more particularly, to a multiple jet ink jet printer in which each jet deposits drops selectively along a plurality of parallel print lines on a moving print receiving medium.
A number of prior art multiple jet printers have provided for servicing a plurality of print positions on a print receiving medium with each of a plurality of jets. Such printers have generally been relatively complicated in structure, and many printers of this type have required cyclically varying drop deflecting fields for deflection of the drops to the multiple print positions. Such rapidly changing fields may be difficult to produce due to the difficulty in switching the relatively large potentials which are applied to the deflection field electrodes.
One such jet printer device is shown in U.s. Pat. No. 3,739,395, issued June 12, 1973, to King. The King printer generates a plurality of jets which are arranged in a row perpendicular to the direction of print web movement. Drops in the jets ae selectively charged on a binary basis. Two pairs of deflection electrodes, associated with each jet, generate deflection fields through which the drops in the jet pass. The uncharged jets pass through the fields in a straight trajectory to a catcher extending beneath the row of jets. The first deflection electrode pair provides a static electrical field which deflects the charged jet drops in a direction substantially perpendicular to the row of jets such that the charged drops do not strike the catcher. Thereafter, the charged drops pass through a field provided by the second pair of electrodes and are laterally deflected in a direction parallel to the row of jets such that they strike the print receiving web along one of a plurality of print lines on the web. This second pair of electrodes has a cyclically varying potential applied thereto, such that a cyclically varying electric field laterally deflects charged drops passing through the field to selected print positions.
U.S. Pat. No. 3,641,588, issued Feb. 8, 1972, to Metz, discloses an ink jet printer in which drops from a row of jet drop streams are selectively charged and the charged drops are deflected substantially perpendicular to the row such that they do not strike a catcher. The charged drops are thereafter laterally deflected generally parallel to the row of jet drop streams such that they strike a continuously moving print receiving medium at one of a plurality of laterally displaced print positions. In order to compensate for movement of the print receiving medium during lateral deflection of the drop streams to produce characters in a substantially square matrix, each pair of deflection electrodes is tilted slightly with resepct to the row of jets. Similarly, the drop catcher for each jet is correspondingly tilted.
U.S. Pat. No. 3,656,174, issued Apr. 11, 1972, to Robertson, discloses a printing device in which a plurality of jet streams from a set of orifices in an orifice plate are spaced apart along a closed contour in the orifice plate. Drops from the streams are selectively charged by application of an electrical signal to a conductive surface surrounding the streams adjacent the point at which the drops are formed. The conductive surface extends beneath the point of drop formation for production outwardly attractive forces on the charged drops. The drops are deflected outwardly for selective catching by an apertured catching plate. By modulating the charging signal, the drops from each jet may be deflected outwardly to selected print positions, thereby creating half-tone images on the print receiving medium below the apertured catched plate.
U.S. Pat. No. 4,123,760, issued Oct. 31, 1978, to Hou, discloses a jet drop recorder, including a plurality of pairs of deflection electrodes which are positioned on opposite sides of respective ones of a plurality of jet fluid filaments and offset with respect to the filaments. Drops formed from the end of each fluid filament are steered to different laterally separated printing positions by application of a cyclic differential electrical signal to the electrodes. This signal deflects the unbroken fluid filament, which in turn directs the drops toward the desired printing positions. No additional field is required since drops are directed to a catcher parallel to the row of jets by applying a signal simultaneously to both of the electrodes in each electrode pair.
U.S. Pat. No. 3,871,004, issued Mar. 11, 1975, to Rittberg, discloses a moving jet drop printer in which ejector nozzles are arranged in a row opposite the record carrier for ejection of the fluid drops by means of selectively excitable pressure generators. Deflection electrodes are positioned adjacent each nozzle and have cyclically varying deflection potentials placed there across in order to produce deflection of drops from each nozzle in a direction which is inclined with respect to the direction of movement of the printer. Each nozzle is therefore capable of servicing a number of print positions.
U.S. Pat. No. 3,596,276, issued July 27, 1971, to Lovelady et al, and IBM Techincal Disclosure Bulletin, Vol. 11, No. 10, March 1969, pp. 1292 and 1293, disclose single jet printers, utilizing a skewed pair of lateral deflection electrodes for generating an inclined static electrical deflection field. The jet drops are charged to varying levels and thereafter deflected by the deflection field. Skewing of the deflection field results in elimination of the skewed print pattern which would otherwise result from simultaneous printing and movement of the print receiving medium.
U.S. Pat. No. 3,298,030, issued Jan. 10, 1967, to Lewis et al, discloses a multiple jet ink jet printer in which the jet streams are positioned in a row perpendicular to the direction of movement of the print receiving medium and in which drops in ech jet are selectively charged to discrete charge levels. Thereafter, the charged drops are deflected to print positions on the print receiving medium by pairs of lateral deflection electrodes, one such pair being positioned adjacent each of the jet streams. The lateral deflection electrodes provide static deflection fields which extend generally in a direction perpendicular to the movement of the print receiving medium. Drops which are to be caught are charged sufficiently such that they are laterally deflected to catchers positioned between the jets and extending parallel to the direction of movement of the print receiving medium. Since a catcher structure is interposed between each of the adjacent jets in the Lewis et al printer, the printer is not capable of providing print coverage across the entire width of the print receiving medium.
U.S. Pat. No. 3,972,052, issued July 27, 1976, to Atumi et al, discloses printing apparatus in which drops from a single jet are selectively charged to a single charge level and thereafter deflected laterally and longitudinally by pairs of deflectin electrodes across which are impressed ramp-shaped deflection signals.
Several prior art ink jet printers include a row of jets which is inclined with respect to the direction of movement of a print receiving medium. While capable of providing printing of multiple print positions with each jet by deflection of drops in a direction perpendicular to the row, such printers generally require substantial reordering of input data. Relatively complicated print control circuitry will therefore generally be required.
U.S. Pat. No. 4,085,409, issued Apr. 18, 1978, to Paranjpe, discloses a jet printer having one or more rows of jets which are deflected in a direction perpendicular to the jet row or rows, such that the drops from each jet strike the print medium at a plurality of print positions. The row of jets is inclined with respect to the direction of movement of the print receiving medium. Drops in the streams are selectively charged to one of a number of discrete charge levels in order to cause the drops to be appropriately deflected by a static electrical field. Drops charged to a catch charge level are deflected by a static electrical field to a catcher which extends parallel to the row. IBM Technical Disclosure Bulletin, Vol. 20, No. 2, dated July 1977, pp. 760, 761, by D.W. Albrecht, discloses a printer similar in operation to the Paranjpe '409 printer.
U.S. Pat. No. 4,122,458, issued Oct. 24, 1978, to Paranjpe, discloses a similar printer arrangement in which drops from each jet pass successively through a plurality of variable deflection fields. Each of the deflection fields extends perpendicular to the row of jets and deflection may be controlled either by charging the jets to varying charge levels, or by altering one or more of the deflection fields in dependence upon the print position to which the drop is to be directed, or by using both techniques simultaneously.
U.S. Pat. No. 4,091,390, issued May 23, 1978, to Smith et al, discloses an ink jet printer in which a row of jet nozzles is inclined with respect to the direction of relative motion of a recording surface to permit selectively charged drops, charged to one of several charge levels, to be deflected by a single pair of electrostatic deflection plates common to all of the nozzles and parallel generally to the row of jets.
It may be seen, therefore, that prior art multiple jet printers, in which each jet services a number of print positions on the print receiving medium, are relatively complicated in structure. A need exists therefore for an ink jet printer of simple construction in which each of a plurality of jets services a number of print positions with the drops in each jet being directed to the respective print positions by means of static electrical fields.